JP7293837B2 - image forming device - Google Patents

Description

The present invention relates to an electrophotographic image forming apparatus having a photosensitive drum and a developing roller.

2. Description of the Related Art Conventionally, as an electrophotographic image forming apparatus, there is known one having a mechanism in which a developing roller contacts and separates from a photosensitive drum as a cam rotates (Patent Document 1).

JP 2012-128017 A

By the way, if the contact time between the developing roller and the photosensitive drum becomes longer than necessary, the toner may stick between the developing roller and the photosensitive drum, or the life of the developing roller may be shortened. Therefore, it is desirable that the contact time between the developing roller and the photosensitive drum is as short as possible.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an image forming apparatus capable of suppressing contact between a developing roller and a photosensitive drum as much as possible.

To achieve the above object, the image forming apparatus of the present invention includes a photosensitive drum, a developing roller movable between a contact position in contact with the photosensitive drum and a spaced position away from the photosensitive drum, and a developing roller in contact with the photosensitive drum. A cam for moving between a position and a separated position, the cam being rotatable in a predetermined rotational direction, a switching mechanism capable of switching between rotation and stoppage of the cam, and at least one sheet tray on which sheets are set. , a supply mechanism that supplies a sheet from a sheet tray toward the photosensitive drum, a sheet sensor capable of detecting the passage of the sheet on the upstream side of the photosensitive drum in the sheet conveying direction, and a control unit.
In the case of forming an image on a sheet, if the sheet sensor detects passage of the trailing edge of the first sheet and a predetermined period of time has passed, the control unit detects that the next second sheet is not conveyed. After the development of the image transferred to one sheet is completed, the switching mechanism is controlled to rotate the cam, thereby moving the developing roller from the contact position to the separated position.
Then, when the image data of the image to be transferred to the second sheet is ready and the predetermined waiting time has passed after the predetermined time has passed, the control unit controls the feeding mechanism to transfer the second sheet. The sheet tray starts to supply the photosensitive drum, and after that, the switching mechanism is controlled according to the conveyance of the second sheet to rotate the cam, thereby moving the developing roller from the separated position to the contact position.

According to such a configuration, when the sheet sensor detects the passage of the trailing edge of the first sheet and the next second sheet is not conveyed when the predetermined time elapses, the first sheet is detected. After the development of the image to be transferred is completed, the developing roller is separated from the photosensitive drum, and then the developing roller is brought into contact with the photosensitive drum again to develop the image to be transferred to the second sheet. contact with the photosensitive drum can be suppressed.

In the above-described image forming apparatus, the standby time is defined as the time when the developing roller starts to separate from the photosensitive drum, the developing roller separates from the photosensitive drum, and then the developing roller comes into contact with the photosensitive drum again, and the surface of the photosensitive drum becomes wet. From the time the development start position reaches the transfer position where the toner image is transferred to the second sheet, from the time the second sheet starts to be fed from the sheet tray, the leading edge of the image forming area of the second sheet reaches the transfer position. It is possible to configure that the time is equal to or longer than the time obtained by subtracting the time until reaching the .

According to this, by supplying the second sheet from the sheet tray after the waiting time has elapsed, the leading edge of the image forming area of the second sheet is reached after the timing at which the development start position on the surface of the photosensitive drum reaches the transfer position. can reach the transfer position. Thus, regardless of the distance from the photosensitive drum along the sheet conveying path of the sheet tray, the developing roller can be brought into contact with the photosensitive drum in time for the transfer of the leading edge of the image forming area of the second sheet.

The above-described image forming apparatus includes a plurality of sheet trays having different distances along the sheet conveying path from the photosensitive drums, and the controller controls the sheet trays having smaller distances along the sheet conveying path from the photosensitive drums. It can be configured to increase the waiting time.

According to this, the second sheet can be supplied from the sheet tray toward the photosensitive drum at the optimum timing according to the position of each sheet tray.

In the above-described image forming apparatus, when the second sheet is being conveyed after a predetermined period of time has elapsed since the sheet sensor detected the passage of the trailing edge of the first sheet, When it is determined that the sheet interval, which is the interval between the trailing edge of the first sheet and the leading edge of the second sheet, is larger than the predetermined interval, the switching mechanism is operated after the development of the image transferred to the first sheet is completed. By controlling and rotating the cam, the developing roller is moved from the contact position to the separated position, and thereafter, the switching mechanism is controlled according to the conveyance of the second sheet to rotate the cam, thereby moving the developing roller from the separated position to the contact position. It can be configured to move to a position.

According to this, contact between the developing roller and the photosensitive drum can be suppressed as much as possible.

In the above-described image forming apparatus, the control unit controls the sheet interval when the second sheet is being conveyed after a predetermined period of time has elapsed since the sheet sensor detected the passage of the trailing edge of the first sheet. When it is determined that the interval is less than or equal to , the image transferred to the second sheet is developed while the developing roller is positioned at the contact position without rotating the cam.

The image forming apparatus described above further includes a motor and a drive transmission mechanism for transmitting a driving force from the motor to the developing roller. The cam is mechanically connected to the drive transmission mechanism, and the drive transmission mechanism is in the contact position, the driving force from the motor is transmitted to the developing roller, and when the developing roller is in the separated position, the driving force from the motor is not transmitted to the developing roller.

According to this, it is possible to suppress contact between the developing roller and the photosensitive drum as much as possible, thereby suppressing the development roller from being positioned at the contact position, thereby suppressing unnecessary rotation of the development roller. can.

In the image forming apparatus described above, the cam is a cam that rotates around an axis parallel to the rotation axis of the developing roller, and has a first cam portion projecting in the direction of the rotation axis of the developing roller. The configuration may further include a developing cartridge having a roller, and a cam follower that comes into contact with the first cam portion of the cam and slides in the rotation axis direction to press the developing cartridge.

The image forming apparatus described above further includes a supporting member that supports the developing cartridge, the developing cartridge having a slide member that is slidable in the rotation axis direction by being pressed by the cam follower, and the slide member is the support member. and urges the developing cartridge in a direction perpendicular to the rotation axis direction.

The image forming apparatus further includes a registration roller which is the closest transport roller to the photosensitive drum among the transport rollers arranged on the upstream side of the photosensitive drum in the transport direction, and the sheet sensor serves as a registration roller in the transport direction. A post-registration sensor may be provided between the roller and the photosensitive drum.

According to the present invention, contact between the developing roller and the photosensitive drum can be suppressed as much as possible.

1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment; FIG. Fig. 2 is a perspective view of a support member, cam and cam follower; It is the perspective view (a) of developer cartridge, and the side view (b). 4A and 4B are schematic top views of the periphery of the developing cartridge for explaining the slide member, showing (a) when the cam follower is at the standby position and (b) when the cam follower is at the operating position; FIG. 4 is a view showing the inner surface (developing cartridge side) of the side frame of the supporting member; FIG. It is the perspective view which looked at the drive transmission mechanism from the upper left. It is the figure which looked at the drive transmission mechanism from the left side along the axial direction. It is the perspective view which looked at the drive transmission mechanism from the upper right. It is the figure which looked at the drive transmission mechanism from the right side along the axial direction. It is the exploded perspective view (a) which looked at the clutch from the sun gear side, and the exploded perspective view (b) which looked at the carrier side. FIG. 10 is an axial view (a) and a perspective view (b) showing the separating mechanism, the lever, the clutch, and the coupling gear when the developing roller is in the contact position and the clutch is in the transmission state; An axial view showing the separation mechanism, lever, clutch, and coupling gear when the cam rotates from the state of FIG. 11 and the developing roller corresponding to yellow is forming an image at the contact position. It is (a) and a perspective view (b). The cam is rotated from the state of FIG. 12, the developing roller is in the separated position, and the clutch is in the transmission state. ) and a perspective view (b). The cam is rotated from the state of FIG. 13, the developing roller is in the separated position, and the clutch is in the disengaged state. ) and a perspective view (b). 14 shows the separating mechanism, the lever, the clutch, and the coupling gear when the cam is rotated from the state of FIG. 14 and is temporarily stopped just before the developing roller corresponding to yellow begins to move to the contact position. , an axial view (a) and a perspective view (b). 5 is a flow chart showing an example of contact/separation processing of the developing roller. 7 is a flowchart illustrating an example of sheet supply processing; 3 is a flow chart (a) showing an example of contact control processing for color printing, and a flow chart (b) showing an example of separation control processing. 4 is a timing chart for explaining control of the YMC clutch and K clutch based on the output of each sensor when color printing is performed; 4 is a timing chart for explaining the operations of cams, separation sensors, and developing rollers for each color when color printing is performed; FIG. 4A is a flow chart showing an example of contact control processing when monochrome printing is performed, and FIG. 4B is a flow chart showing an example of separation control processing. 5 is a timing chart for explaining control of the K clutch and operation of the black developing roller based on the outputs of each sensor when monochrome printing is performed; 7A to 7D are diagrams (a) to (d) for explaining the separating and contacting operations of the developing rollers in the case of color printing. FIG. 24A to 24D following FIG. 23 for explaining the separating and contacting operations of the developing rollers in the case of color printing; FIG. 10A to 10C are diagrams (a) to (c) for explaining the separating and contacting operations of the developing roller in the case of monochrome printing. FIG. 2 is a timing chart for explaining the output of each sensor and the operation of the paper feed roller, YMC clutch, and development roller for each color when color printing is performed continuously on a plurality of sheets. Indicates the case of supply. A timing chart for explaining the output of each sensor and the operation of the paper feed roller, YMC clutch, and developing rollers for each color when color printing is performed continuously on multiple sheets. The next sheet is supplied from the manual feed tray. indicates when 2 is a timing chart for explaining the output of each sensor and the operation of the paper feed roller, YMC clutch, and developing roller for each color when color printing is performed continuously on a plurality of sheets; Indicates the case of supply.

As shown in FIG. 1, the image forming apparatus 1 according to the embodiment is a color printer, and mainly includes a sheet feeding section 20, an image forming section 30, and a control section 2 inside a main housing 10. there is

The sheet supply unit 20 is provided in the lower part of the main body housing 10, and includes a first tray 21, a second tray 31, and a manual feed tray 41 as a plurality of sheet trays on which the sheets S are set. A supply mechanism 22 is provided for supplying from 31 and 41 toward the image forming section 30 (photosensitive drum 50). The first tray 21 and the second tray 31 are configured to be removable from the main housing 10 by being pulled out to the left side in FIG. The first tray 21 and the second tray 31 are arranged at the bottom inside the main body housing 10 , and the second tray 31 is arranged below the first tray 21 . The second tray 31 is a sheet tray added below the first tray 21 . The manual feed tray 41 is provided above the first tray 21 and on the front side of the image forming section 30 . The trays 21, 31, and 41 have different distances along the conveying path (see two-dot chain line) of the sheet S from the photosensitive drum 50 (50Y). Specifically, the second tray 31 has a greater distance along the transport path of the sheet S from the photosensitive drum 50 (50Y) than the first tray 21, and the manual feed tray 41 has a distance from the photosensitive drum 50 (50Y). The distance along the conveying path of the sheet S is smaller than that of the first tray 21 .

The supply mechanism 22 is provided in the front part of the main body housing 10, and includes paper feed rollers 23, 33, 43, separation rollers 24, 34, separation pads 25, 35, transport rollers 26, 36, and a registration mechanism. A roller 27 is provided. The registration roller 27 is the closest transport roller to the photosensitive drum 50 (50Y) among the transport rollers for transporting the sheet S arranged on the upstream side of the photosensitive drum 50 (50Y) in the transport direction of the sheet S. . In this specification, for the sake of convenience, directions such as front and back are described with the left side of FIG. That is, the left side of FIG. 1 is the front, the right side is the rear, and the top and bottom are the top and bottom. A sheet S in this specification is a medium on which an image can be formed by the image forming apparatus 1, and includes plain paper, envelopes, postcards, thin paper, thick paper, glossy paper, resin sheets, stickers, and the like.

In the sheet supply unit 20 , the sheets S stored in the first tray 21 are fed out by the paper feed roller 23 and then separated one by one between the separation roller 24 and the separation pad 25 . Also, the sheets S accommodated in the second tray 31 are separated one by one between the separation roller 34 and the separation pad 35 after being sent out by the paper feed roller 33 . Also, the sheet S set on the manual feed tray 41 is sent out by the paper feed roller 43 . After that, the leading edge position of the sheet S is regulated by the registration rollers 27 that are not rotating, and then the registration rollers 27 are rotated to supply the sheet S to the image forming section 30 .

On the upstream side of the photosensitive drum 50 (50Y) in the conveying direction of the sheet S, paper feed sensors 28A and 38A capable of detecting passage of the sheet S, pre-registration sensors 28B and 48B, and a post-registration sensor 28C as a sheet sensor are arranged. It is The pre-registration sensor 28B is provided downstream of the paper feed sensors 28A and 38A and upstream of the registration roller 27 in the sheet S conveying direction. Specifically, the pre-registration sensor 28 B is provided between the conveying roller 26 and the registration roller 27 . The pre-registration sensor 48B is provided upstream of the registration roller 27 in the sheet S conveying direction. Specifically, the pre-registration sensor 28 B is provided between the manual feed tray 41 and the registration roller 27 .

The post-registration sensor 28C is provided between the registration roller 27 and the photosensitive drum 50 (50Y) in the sheet S conveying direction. The paper feed sensor 28A is a sensor that first detects passage of the sheet S fed from the first tray 21, and is provided between the separation roller 24 and the transport roller 26. As shown in FIG. The paper feed sensor 38A is a sensor that first detects passage of the sheet S fed from the second tray 31, and is provided between the separation roller 34 and the transport roller 36. As shown in FIG.

The image forming section 30 includes an exposure device 40 , a plurality of photosensitive drums 50 , a plurality of developing cartridges 60 , a conveying device 70 and a fixing device 80 .

The exposure device 40 has a laser diode, a deflector, a lens and a mirror (not shown). The exposure device 40 is configured to emit a plurality of laser beams for exposing a plurality of photosensitive drums 50 to scan the surfaces of the photosensitive drums 50 .

The photosensitive drums 50 include a first photosensitive drum 50Y corresponding to yellow as an example of a first color, a second photosensitive drum 50M corresponding to magenta as an example of a second color, and a cyan as an example of a third color. A corresponding third photosensitive drum 50C and a fourth photosensitive drum 50K corresponding to black, which is an example of the fourth color, are included. In the present specification and drawings, members provided corresponding to the respective colors of yellow, magenta, cyan, and black are denoted by Y, M, C, and K, respectively, when distinguishing the colors. is shown. On the other hand, when the description is made without distinguishing the colors, the symbols Y, M, C, and K are omitted, and the names such as first and second are omitted.

A developing cartridge 60 is provided corresponding to each photosensitive drum 50 . Specifically, the developing cartridge 60 includes a first developing cartridge 60Y having a first developing roller 61Y that supplies toner to the first photosensitive drum 50Y, and a second developing roller 61M that supplies toner to the second photosensitive drum 50M. a third developing cartridge 60C having a third developing roller 61C that supplies toner to the third photosensitive drum 50C; and a fourth developing roller 61K that supplies toner to the fourth photosensitive drum 50K. 4 developer cartridge 60K.

The first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are arranged in this order from upstream to downstream in the sheet S movement direction.

Each developing cartridge 60 is located at a contact position where the developing roller 61 contacts the corresponding photosensitive drum 50, indicated by a solid line in FIG. It is movable to and from a position in a spaced position spaced apart from 50 . Then, when the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are at the separated positions, the second developing cartridge 60M, the third developing cartridge 60C, and the fourth developing cartridge 60K move the sheet S It overlaps with the optical path of the laser beam that exposes the photosensitive drum 50 adjacent to the upstream side in the moving direction. Specifically, when the second developing roller 61M is at the spaced position, the second developing cartridge 60M overlaps the optical path of the laser beam that exposes the first photosensitive drum 50Y, and the third developing cartridge 60C is the third developing cartridge. When the roller 61C is at the separated position, it overlaps with the optical path of the laser beam that exposes the second photosensitive drum 50M. overlaps the optical path of the laser beam that exposes the .

As shown in FIG. 2, the photosensitive drum 50 is rotatably supported by a supporting member 90. As shown in FIG. The supporting member 90 detachably supports the first developing cartridge 60Y, the second developing cartridge 60M, the third developing cartridge 60C, and the fourth developing cartridge 60K. The support member 90 can be attached to and detached from the main housing 10 through an opening formed by opening the front cover 11 (see FIG. 1) of the main housing 10 . The support member 90 includes a pair of side frames 91 spaced apart in the axial direction of the photosensitive drum 50, a connecting frame 92 connecting the front portions of the pair of side frames 91, and the rear portions of the pair of side frames 91. and a connecting frame 93 to be connected. The pair of side frames 91 includes a right side frame 91R and a left side frame 91L. The support member 90 is provided with chargers 52 (see FIG. 1) for charging the photosensitive drums 50 arranged opposite to the respective photosensitive drums 50 .

The image forming apparatus 1 arranges the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K at contact positions where they contact the corresponding photosensitive drums 50 among the plurality of photosensitive drums 50, It has a separation mechanism 5 for moving between a separation position separated from the photosensitive drum 50 . The spacing mechanism 5 is provided for each of the first color, second color, third color and fourth color.

Specifically, each spacing mechanism 5 includes a cam 150 (150Y, 150M, 150C, 150K) rotatable around an axis parallel to the rotation axis 61X (see FIG. 1) of the developing roller 61, and a cam follower 170.
The cam 150 rotates in a predetermined rotational direction when a driving force is transmitted from the motor 3 (see FIG. 9). The cam 150 has a first cam portion 152A that protrudes in the direction of the rotation axis of the developing roller 61 (hereinafter simply referred to as "the direction of the rotation axis").
The cam follower 170 comes into contact with the cam surface 152F, which is the end surface of the first cam portion 152A of the cam 150, and moves between the operating position shown in FIG. , and a standby position where the developing roller 61 is positioned at the contact position. The cam follower 170 comes into contact with the first cam portion 152A of the cam 150 and slides in the direction of the rotation axis to be positioned at the operating position. One of the developing cartridges 60K is pressed. Also, the cam follower 170 is separated from the developer cartridge 60 at the standby position.

Returning to FIG. 2, the cam 150 and cam follower 170 are provided corresponding to each developing cartridge 60 . Cam 150 and cam follower 170 are arranged laterally outside of left side frame 91L. Detailed structures of the cam 150 and the cam follower 170 will be described later.

The support member 90 is provided with a contact portion 94 that contacts a slide member 64, which will be described later, on the upper portions of the side frames 91R and 91L. The abutted portion 94 is arranged, for example, around an axis along a third direction (vertical direction) orthogonal to both a first direction parallel to the axial direction of the photosensitive drum 50 and a second direction in which the photosensitive drums 50 are arranged. It consists of rotatable rollers.

The support member 90 also includes a pressing member 95 provided corresponding to each developing cartridge 60 . The pressing members 95 are provided at both ends of the photosensitive drum 50 in the axial direction for each developing cartridge 60 . The pressing member 95 is urged rearward by a spring 95A (see FIGS. 4A and 4B). By pressing, the developing roller 61 is brought into pressure contact with the corresponding photosensitive drum 50 .

As shown in FIGS. 3A and 3B, the developer cartridge 60 (60Y, 60M, 60C, 60K) has a case 63 containing toner, a slide member 64, and a coupling 65. As shown in FIG.

The case 63 has a first protrusion 63A and a second protrusion 63B on one side surface as protrusions protruding in the rotation axis direction.
The first protrusion 63A is arranged coaxially with the rotation axis 61X of the developing roller 61 and protrudes in the direction of the rotation axis.
The second projecting portion 63B is arranged at a predetermined distance from the first projecting portion 63A. In this embodiment, the second projecting portion 63B is arranged above the first projecting portion 63A.
Both the first projecting portion 63A and the second projecting portion 63B are rollers rotatable around an axis parallel to the rotation axis direction.
Although not shown, the case 63 is also provided with a first projecting portion 63A and a second projecting portion 63B on the other side surface at positions symmetrical to the one side surface.

Further, the case 63 has a protrusion 63D pressed by the pressing member 95 on the upper portion of the front surface. The protrusions 63D are provided at both ends of the case 63 in the rotation axis direction.

The coupling 65 engages with a coupling shaft 119 to be described later, and receives rotational driving force from the coupling shaft 119 .

The slide member 64 is a member that can slide in the rotation axis direction with respect to the case 63 . The slide member 64 is slidable in the rotational axis direction by being pressed by the cam follower 170 .

As shown in FIGS. 4A and 4B, the slide member 64 includes a shaft 181, a first contact member 182, and a second contact member 183. As shown in FIGS. The first contact member 182 is fixed to one end of the shaft 181 and the second contact member 183 is fixed to the other end of the shaft 181 .

The shaft 181 is disposed through a hole formed in the case 63 and extending in the rotation axis direction, and is slidably supported by the case 63 .

The first contact member 182 has a pressing surface 182A, which is an end surface in the rotation axis direction, and an inclined surface 182B inclined with respect to the rotation axis direction.
The pressing surface 182A is a surface pressed by the cam follower 170. As shown in FIG.
When the slide member 64 is pressed in the rotation axis direction by the cam follower 170, the inclined surface 182B abuts against the abutted portion 94 of the support member 90, and moves the developing cartridges 60 (60Y, 60M, 60C, 60K) along the rotation axis. The developing cartridge 60 is moved in a direction orthogonal to the direction, specifically, in a direction parallel to the moving direction of the sheet S (see FIG. 4B). The slope 182B is inclined from one end to the other end of the shaft 181 so as to be positioned in the direction (forward) from the photosensitive drum 50 toward the corresponding developing roller 61 in the second direction.

The second contact member 183 has a slope 183B that is slanted like the slope 182B of the first contact member 182 . When the slide member 64 is pressed in the rotation axis direction by the cam follower 170, the inclined surface 183B is also brought into contact with the abutted portion 94 of the support member 90, and the developing cartridges 60 (60Y, 60M, 60C, 60K) are moved onto the sheet S. A force is applied in a direction parallel to the moving direction to move the developing cartridge 60 (see FIG. 4B).

A spring 184 is arranged between the first contact member 182 and the case 63 to bias the slide member 64 toward one side of the rotation axis direction, that is, leftward in this case. The spring 184 is a compression coil spring and is arranged outside the shaft 181 so that the shaft 181 passes through the coil.

As shown in FIG. 5, the support member 90 has a first support surface 96A and a second support surface 96B as support surfaces on the inner surface of one side frame 91L. When the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K move from the contact position to the separated position, the first support surface 96A and the second support surface 96B move from the contact position to the separated position. The projecting portion 63A and the second projecting portion 63B are supported from below. The first support surface 96A and the second support surface 96B extend in the sheet S moving direction.
The first support surface 96A is arranged to support the first protrusion 63A. The first support surface 96</b>A also functions to guide and vertically position the developing roller 61 when the developing cartridge 60 is attached to the supporting member 90 .
The second support surface 96B is arranged above the first support surface 96A so as to support the second protrusion 63B.
Although not shown, the support member 90 also has a first support surface 96A and a second support surface 96B on the inner surface of the other side frame 91R, which are bilaterally symmetrical with the one side frame 91L.

When the developing roller 61 is positioned at the contact position where the developing roller 61 contacts the photosensitive drum 50, the first projecting portion 63A of the first developing cartridge 60Y, the second developing cartridge 60M and the third developing cartridge 60C shown in FIG. It is located toward the rear in 96A. On the other hand, when the developing roller 61 is positioned at the spaced position away from the photosensitive drum 50, the first projecting portion 63A is positioned toward the front of the first support surface 96A, like the fourth developing cartridge 60K in FIG.
In this manner, the separating mechanism 5 moves the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K from the contact position to the separated position. 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are moved from the downstream side to the upstream side in the sheet S moving direction.

As shown in FIGS. 11A and 11B, the cam 150 has a disk portion 151, a gear portion 150G, an end face cam 152, and a clutch control cam 153. As shown in FIGS. The cam 150 is a member that rotates to move the corresponding developing roller 61 between the contact position and the separated position.

The disk portion 151 has a substantially disk shape and is rotatably supported by the support plate 102 (see FIG. 8).
The gear portion 150G is formed on the outer circumference of the disk portion 151. As shown in FIG.
The end face cam 152 has a first cam portion 152A that is a portion that protrudes from the disk portion 151 and constitutes the spacing mechanism 5 for the developing roller 61 . The end face cam 152 has a cam face 152F on its end face in the rotation axis direction.
The cam surface 152F has a first holding surface F1, a second holding surface F2, a first guide surface F3, and a second guide surface F4.
The first holding surface F1 holds the cam follower 170 at the standby position.
The second retaining surface F2 retains the cam follower 170 in the operating position.
The first guide surface F3 is a surface that connects the first holding surface F1 and the second holding surface F2 and is inclined with respect to the first holding surface F1. The first guide surface F3 guides the cam follower 170 from the first holding surface F1 to the second holding surface F2 as the cam 150 rotates.
The second guide surface F4 is a surface that connects the second holding surface F2 and the first holding surface F1 and is inclined with respect to the first holding surface F1. The second guide surface F4 guides the cam follower 170 from the second holding surface F2 to the first holding surface F1 as the cam 150 rotates.

The clutch control cam 153 is a part that cooperates with the lever 160 to switch transmission/disengagement of the clutch 120 . The clutch control cam 153 has a cylindrical base circular portion 153A and a second cam portion 153B protruding in the diameter direction of the cam 150 from the base circular portion 153A. The clutch control cam 153 is formed integrally with the disc portion 151 . Therefore, the second cam portion 153B rotates together with the cam 150. As shown in FIG.

The cam follower 170 has a slide shaft portion 171 and a contact portion 172 .
The slide shaft portion 171 is slidably supported by a shaft portion (not shown) fixed to the main housing 10, and is slidable in the direction of the rotation axis. The slide shaft portion 171 is biased in a direction in which the contact portion 172 contacts the cam surface 152</b>F of the cam 150 by a spring 173 that is a biasing member. The cam follower 170 is thereby urged toward the standby position. The spring 173 is a tension coil spring, one end of which is hooked to the slide shaft portion 171 and the other end of which is hooked to a spring mounting portion (not shown) provided inside the main housing 10 .
The contact portion 172 is provided to extend from the slide shaft portion 171 . The end surface of the contact portion 172 in the rotation axis direction faces the cam surface 152F and can come into contact with the cam surface 152F.

As shown in FIG. 8, the cams 150Y, 150M, 150C, and 150K differ from each other in that only the cam 150Y has a longer length in the rotational direction of the cam 150 of the first cam portion 152A than the others. are almost the same.
Each of the cams 150C and 150K has a detected portion 154 projecting axially from the disk portion 151 at a position closer to the center of rotation than the first cam portion 152A. The body housing 10 is provided with separation sensors 4K and 4C corresponding to black and cyan.
The separation sensors 4K, 4C are phase sensors that detect the phases of the cams 150C, 150K. The separation sensors 4K and 4C output separation signals when the cams 150C and 150K are positioned within a predetermined phase range in which the third developing roller 61C and the fourth developing roller 61K are separated. does not output a separation signal if it is not positioned within the phase range of In this embodiment, for the sake of convenience, the case of outputting the separation signal is called ON, and the case of not outputting the separation signal is called OFF. It does not matter which voltage is higher when the separation signal is output or when it is not output.

The separation sensors 4K and 4C have a light-emitting portion 4P that emits detection light and a light-receiving portion 4R that can receive the detection light from the light-emitting portion 4P. The separation sensors 4K and 4C control the ON signal when the detected portion 154 enters between the light emitting portion 4P and the light receiving portion 4R and blocks the detection light of the light emitting portion 4P and the light receiving portion 4R does not receive the detection light. 2, and outputs an OFF signal to the control unit 2 when the detection light from the light emitting unit 4P is received by the light receiving unit 4R from between the light emitting unit 4P and the light receiving unit 4R. Although the cams 150Y and 150M are also provided with the same shape as the detected portion 154, they do not function as the detected portion because no separation sensor corresponding to the cams 150Y and 150M is provided.

Returning to FIG. 1 , the conveying device 70 is provided between the first tray 21 and the photosensitive drum 50 . The conveying device 70 includes a driving roller 71 , a driven roller 72 , a conveying belt 73 made up of an endless belt, and four transfer rollers 74 . The conveying belt 73 is stretched between the driving roller 71 and the driven roller 72 , and the outer surface of the conveying belt 73 faces the photosensitive drums 50 . Each transfer roller 74 is arranged inside the conveying belt 73 so as to sandwich the conveying belt 73 with each photosensitive drum 50 . The conveying device 70 conveys the sheet S by moving the conveying belt 73 with the sheet S placed on the outer peripheral surface of the upper side.

The fixing device 80 is provided behind the photosensitive drum 50 and the conveying device 70 . The fixing device 80 includes a heating roller 81 and a pressure roller 82 arranged to face the heating roller 81 . A discharge sensor 28D for detecting passage of the sheet S is provided downstream of the fixing device 80 in the direction in which the sheet S is conveyed. A conveying roller 15 is provided above the fixing device 80 , and a discharge roller 16 is provided above the conveying roller 15 .

In the image forming section 30 configured as described above, the surface of each photosensitive drum 50 is first uniformly charged by the charger 52 and then exposed to light emitted from each exposure device 40 . As a result, an electrostatic latent image is formed on each photosensitive drum 50 based on the image data.

The toner in the case 63 is carried on the surface of the developing roller 61 and supplied to the electrostatic latent image formed on the photosensitive drum 50 when the developing roller 61 faces and contacts the photosensitive drum 50 . Thereby, a toner image is formed on the photosensitive drum 50 .

Next, the sheet S supplied onto the conveying belt 73 passes between each photosensitive drum 50 and each transfer roller 74, whereby the toner image formed on each photosensitive drum 50 is transferred onto the sheet S. be. As the sheet S passes between the heating roller 81 and the pressure roller 82 , the toner image transferred onto the sheet S is thermally fixed to the sheet S.

The sheet S ejected from the fixing device 80 is accumulated on the sheet ejection tray 13 on the upper surface of the main housing 10 by the transport roller 15 and the ejection roller 16 .

Next, details of a configuration for driving/stopping the developing roller 61 and a configuration for moving the developing roller 61 into contact with/separate from the photosensitive drum 50 will be described.
As shown in FIGS. 6 and 7, the image forming apparatus 1 applies driving force to the motor 3 and the motor 3 to the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K. and a drive transmission mechanism 100 for transmission. The cam 150 that is part of the separation mechanism 5 is mechanically connected to the drive transmission mechanism 100 . The drive transmission mechanism 100 transmits the driving force from the motor 3 to the developing roller 61 when the developing roller 61 is at the contact position, and transmits the driving force from the motor 3 to the developing roller 61 when the developing roller 61 is at the separated position. is configured not to transmit to

The drive transmission mechanism 100 includes a drive transmission gear train 100D for transmitting the driving force of the motor 3 to the developing roller 61, as shown in FIG. It is mechanically connected to the control gear train 100C. In FIGS. 7 and 9, meshing between the gears of the drive transmission gear train 100D is indicated by thick solid lines, and meshing between the gears of the drive control gear train 100C is shown by thick dashed lines.

The drive transmission gear train 100D includes two first idle gears 110 (110A, 110B), three second idle gears 113A, 113B, 113C, a third idle gear 115 (115Y, 115M, 115C, 115K), It includes four clutches 120 and four coupling gears 117 (117Y, 117M, 117C, 117K). Each gear constituting the drive transmission gear train 100</b>D is supported by the support plate 102 or a frame (not shown) and is rotatable around a rotation axis parallel to the axial direction of the photosensitive drum 50 .

The motor 3 has a rotationally driven output shaft 3A. A gear (not shown) is provided on the output shaft 3A.

As shown in FIG. 6, the first idle gear 110 is a two-stage gear including a large-diameter gear 110L and a small-diameter gear 110S having fewer teeth than the large-diameter gear 110L. The large-diameter gear 110L and the small-diameter gear 110S rotate together. The two first idle gears 110 include a first idle gear 110A arranged on the front side of the output shaft 3A and a first idle gear 110B arranged on the rear side of the output shaft 3A. The small diameter gear 110S of each first idle gear 110 meshes with the gear of the output shaft 3A.

As shown in FIG. 7, the second idle gear 113A meshes with the small diameter gear 110S of one of the first idle gears 110 arranged on the front side.
The second idle gear 113B meshes with the small diameter gear 110S of the other first idle gear 110 arranged on the rear side.

The third idle gears 115Y, 115M, 115C, and 115K are provided corresponding to each color and arranged in this order from front to back.
Each of the third idle gears 115Y and 115M meshes with the second idle gear 113A.
The third idle gear 115C meshes with the second idle gear 113B.
The third idle gear 115C and the third idle gear 115K are each meshed with the second idle gear 113C. As a result, the third idle gear 115K receives driving force from the third idle gear 115C via the second idle gear 113C.

The four clutches 120 each have the same configuration. Each clutch 120 meshes with one of third idle gears 115Y, 115M, 115C and 115K and receives driving force from third idle gear 115. As shown in FIG. The configuration of clutch 120 will be described later.

Each coupling gear 117 meshes with one of the clutches 120 . Each coupling gear 117 has a coaxial coupling shaft 119 that rotates together (see FIG. 6). The coupling shaft 119 is axially movable in conjunction with the opening and closing of the front cover 11, and engages with the coupling 65 (see FIG. 3A) of the developing cartridge 60 when the front cover 11 is closed.

With such drive transmission gear train 100D, yellow coupling gear 117Y receives driving force from motor 3 via first idle gear 110A, second idle gear 113A, third idle gear 115Y and clutch 120. .
Driving force is transmitted from the motor 3 to the magenta coupling gear 117M via the first idle gear 110A, the second idle gear 113A, the third idle gear 115M and the clutch 120. FIG.
Driving force is transmitted from the motor 3 to the cyan coupling gear 117C via the first idle gear 110B, the second idle gear 113B, the third idle gear 115C and the clutch 120. As shown in FIG.
Further, the black coupling gear 117K receives driving force from the motor 3 through the first idle gear 110B, the second idle gear 113B, the third idle gear 115C, the second idle gear 113C, the third idle gear 115K and the clutch 120. is transmitted.

As shown in FIGS. 8 and 9, the drive control gear train 100C includes two fourth idle gears 131 (131A, 131B), two fifth idle gears 132 (132A, 132B), and an example of a switching mechanism. a YMC clutch 140A and a K clutch 140K, two sixth idle gears 133 (133A, 133B), a seventh idle gear 134, an eighth idle gear 135, a ninth idle gear 136, and a tenth idle gear 137 and cams 150 (150Y, 150M, 150C, 150K). Each gear constituting the drive control gear train 100</b>C is supported by the support plate 102 or a frame (not shown) and is rotatable around a rotation axis parallel to the axial direction of the photosensitive drum 50 .

The fourth idle gear 131 is a two-stage gear including a large-diameter gear 131L and a small-diameter gear 131S having fewer teeth than the large-diameter gear 131L (see FIG. 8). The large diameter gear 131L and the small diameter gear 131S rotate together. The two fourth idle gears 131 include a fourth idle gear 131A arranged on the front side of the first idle gear 110A and a fourth idle gear 131B arranged on the rear side of the first idle gear 110B. The large diameter gear 131L of each fourth idle gear 131 meshes with the small diameter gear 110S of the first idle gear 110 .

The two fifth idle gears 132 include a fifth idle gear 132A arranged on the front side of the fourth idle gear 131A and a fifth idle gear 132B arranged on the rear side of the fourth idle gear 131B. Each of the fifth idle gears 132A, 132B meshes with the small diameter gear 131S of the fourth idle gears 131A, 131B.

The YMC clutch 140A switches transmission/disconnection of the driving force of the drive control gear train 100C, which is a system that transmits the driving force to the cams 150 of yellow, magenta and cyan. That is, the YMC clutch 140A can switch rotation/stop of the cams 150Y, 150M, and 150C. The YMC clutch 140A includes a large-diameter gear 140L and a small-diameter gear 140S having fewer teeth than the large-diameter gear 140L. The YMC clutch 140A is arranged in front of the fifth idle gear 132A, and the large diameter gear 140L meshes with the fifth idle gear 132A.
The YMC clutch 140A is, for example, an electromagnetic clutch. When energized (turned ON), the large-diameter gear 140L and the small-diameter gear 140S rotate together. idling and the small diameter gear 140S does not rotate.

The K clutch 140K has the same configuration as the YMC clutch 140A. The K clutch 140K switches transmission/disconnection of the driving force of the drive control gear train 100C of the system that transmits the driving force to the cam 150 of black. That is, the K-clutch 140K can switch between rotating and stopping the cam 150K. The K clutch 140K includes a large-diameter gear 140L and a small-diameter gear 140S having fewer teeth than the large-diameter gear 140L. The K clutch 140K is arranged behind the fifth idle gear 132B, and the large diameter gear 140L meshes with the fifth idle gear 132B.

The sixth idle gear 133 is a two-stage gear including a large-diameter gear 133L and a small-diameter gear 133S having fewer teeth than the large-diameter gear 133L (see FIG. 6). The large diameter gear 133L and the small diameter gear 133S rotate together. The two sixth idle gears 133 include a sixth idle gear 133A arranged on the front side of the YMC clutch 140A and a sixth idle gear 133B arranged on the rear side of the K clutch 140K. The large diameter gear 133L of each sixth idle gear 133 meshes with the small diameter gear 140S of the YMC clutch 140A or K clutch 140K.

The seventh idle gear 134 is arranged between the sixth idle gear 133A and the cam 150Y. The seventh idle gear 134 meshes with the small diameter gear 133S (see FIG. 6) of the sixth idle gear 133A and the gear portion 150G of the cam 150Y.

The eighth idle gear 135 is arranged between the cam 150Y and the cam 150M. The eighth idle gear 135 meshes with the gear portion 150G of the cam 150Y and the gear portion 150G of the cam 150M.

The ninth idle gear 136 is arranged between the cam 150M and the cam 150C. The ninth idle gear 136 meshes with the gear portion 150G of the cam 150M and the gear portion 150G of the cam 150C.

The tenth idle gear 137 is arranged between the sixth idle gear 133B and the cam 150K. The tenth idle gear 137 meshes with the small diameter gear 133S (see FIG. 6) of the sixth idle gear 133B and the gear portion 150G of the cam 150Y.

With such drive control gear train 100C, yellow cam 150Y is driven from motor 3 to first idle gear 110A, fourth idle gear 131A, fifth idle gear 132A, YMC clutch 140A, sixth idle gear 133A and seventh idle gear 133A. Driving force is transmitted via an idle gear 134 .
Further, the magenta cam 150</b>M receives driving force from the yellow cam 150</b>Y through the eighth idle gear 135 .
Further, the cyan cam 150</b>C receives driving force from the magenta cam 150</b>M through the ninth idle gear 136 .
By energizing the YMC clutch 140A, the cams 150Y, 150M, 150C rotate simultaneously, and by stopping the energization of the YMC clutch 140A, the cams 150Y, 150M, 150C all stop.

On the other hand, the black cam 150K receives driving force from the motor 3 via the first idle gear 110B, fourth idle gear 131B, fifth idle gear 132B, K clutch 140K, sixth idle gear 133B and tenth idle gear 137. is transmitted.
By energizing the K clutch 140K, the cam 150K rotates, and by stopping the energization of the K clutch 140K, the cam 150K stops.

Here, the configuration and function of clutch 120 will be described.
As shown in FIGS. 10(a) and 10(b), the clutch 120 has a planetary gear mechanism. The clutch 120 is configured to be switchable between a transmission state in which the driving force from the motor 3 is transmitted to the developing roller 61 and a disconnected state in which the driving force from the motor 3 is not transmitted to the developing roller 61 . Specifically, the clutch 120 includes a sun gear 121 , a ring gear 122 and a carrier 123 that are rotatable about one axis, and a planetary gear 124 supported by the carrier 123 .

The sun gear 121 has a disc portion 121B that rotates integrally with the gear portion 121A, and a plurality of claw portions 121C provided on the outer circumference of the disc portion 121B. The claw portion 121C has a sharp tip, and this sharp tip is inclined in one rotational direction in the circumferential direction.
The ring gear 122 has an inner gear 122A provided on the inner peripheral surface and an input gear 122B provided on the outer peripheral surface.

Carrier 123 has four shafts 123A that rotatably support planetary gear 124 . Further, the carrier 123 is provided with an output gear 123B on its outer peripheral surface.

Four planetary gears 124 are provided, and each of them is rotatably supported by the shaft portion 123A of the carrier 123 . The planetary gear 124 meshes with the gear portion 121 A of the sun gear 121 and also meshes with the inner gear 122 A of the ring gear 122 .

Clutch 120 has input gear 122B in mesh with third idle gear 115 and output gear 123B in mesh with coupling gear 117 (see FIG. 6).
In a state in which the sun gear 121 is stopped so as not to rotate, a transmission state is established in which the driving force input to the input gear 122B can be transmitted to the output gear 123B.
On the other hand, when the sun gear 121 is rotatable, it is in a disconnected state in which the driving force input to the input gear 122B cannot be transmitted to the output gear 123B.
When the driving force is input to the input gear 122B while the clutch 120 is disengaged and the load is applied to the output gear 123B, the output gear 123B does not rotate and the sun gear 121 idles.

As shown in FIG. 9, the drive transmission mechanism 100 further includes a lever 160. As shown in FIG. Lever 160 is swingably supported by support shaft 102A fixed to support plate 102 .
The lever 160 cooperates with the cam 150 to engage the sun gear 121, which is one of the elements of the planetary gear mechanism, the ring gear 122, and the carrier 123, so that the sun gear 121 does not rotate. It has a function of restricting, setting the clutch 120 to the transmitting state, disengaging from the sun gear 121, and setting the clutch 120 to the disengaged state.

Specifically, as shown in FIG. 11A, the lever 160 includes a rotation support portion 161, a first arm 162 extending from the rotation support portion 161, and a direction different from the first arm 162 extending from the rotation support portion 161. and a second arm 163 .

The rotation support portion 161 has a cylindrical shape, and the support shaft 102A of the support plate 102 is placed inside and supported by the support shaft 102A.

The tip of second arm 163 extends toward the outer peripheral surface of disk portion 121B of clutch 120 . The tip of the lever 160 is urged by a torsion spring (not shown) toward the outer peripheral surface of the sun gear 121 (disk portion 121B). The second arm 163 has a hook 163A at its tip. Hook 163A can engage with claw portion 121C on the outer peripheral surface of sun gear 121 to restrict rotation of sun gear 121 .

A distal end portion 162A of the first arm 162 of the lever 160 can come into contact with the second cam portion 153B. The lever 160 has an engagement position where the tip portion 162A of the first arm 162 faces the circular base portion 153A and the hook 163A engages with the pawl portion 121C of the clutch 120, and an engagement position where the tip portion 162A of the first arm 162 is positioned at the second position. By coming into contact with the cam portion 153B and being pushed, the hook 163A can move to a detached position from the claw portion 121C of the sun gear 121, which is one element of the planetary gear mechanism. When the lever 160 is separated from the second cam portion 153B and positioned at the engaged position, the clutch 120 is in the transmission state, and when the lever 160 contacts the second cam portion 153B and is positioned at the disengaged position, the clutch 120 is in the disengaged state. do.

This operation will be described with reference to FIGS. 11 to 15. FIG. Each member shown in FIGS. 11 to 15 corresponds to yellow, but for other colors, the basic operation is the same except that the cam 150 has a different phase.

As shown in FIGS. 11A and 11B, the distal end portion 162A of the first arm 162 faces the circular base portion 153A after separating from the second cam portion 153B. Then, the hook 163A of the second arm 163 is engaged with the pawl portion 121C of the sun gear 121 of the clutch 120, and the lever 160 is positioned at the engagement position. Since the rotation of the sun gear 121 is stopped by the lever 160, the clutch 120 is in a transmission state in which the output gear 123B rotates when the input gear 122B is rotated. As a result, the driving force from the motor 3 can be transmitted to the developing roller 61, and when the motor 3 rotates, the developing roller 61 rotates via the drive transmission gear train 100D. In addition, the cam follower 170 has an end surface of the contact portion 172 positioned on the first holding surface F1 of the cam surface 152F. Therefore, the slide shaft portion 171 is separated from the slide member 64 of the developing cartridge 60 (see FIG. 4A). Therefore, the developing roller 61 is positioned at the contact position.

As shown in FIGS. 12A and 12B, when the cam 150 rotates from the state shown in FIGS. 11A and 11B, the contact portion 172 of the cam follower 170 slides on the first holding surface F1, Approach the guide surface F3. Of the four cams 150, when the yellow cam 150Y is stopped while the developing roller 61 is at the contact position, the contact portion 172 as shown in FIGS. Stop at a position where it touches F3.

When the developing roller 61 is separated from the photosensitive drum 50, the cam 150Y rotates further, and the contact portion 172 slides on the first guide surface F3 and is pushed by the first guide surface F3, thereby causing a As shown in b), the contact portion 172 contacts the second holding surface F2. At this time, the slide shaft portion 171 pushes the slide member 64 of the developer cartridge 60 in the rotation axis direction. Then, the developer cartridge 60 is pushed forward by the reaction force of the support member 90 (see FIG. 4B). The developing roller 61 is separated from the photosensitive drum 50 when the contact portion 172 is located near the second holding surface F2 of the first guide surface F3. When the contact portion 172 contacts the second holding surface F2, the developing roller 61 is held at the separated position.

As shown in FIGS. 14(a) and 14(b), after the developing roller 61 is positioned at the separated position, the cam 150 rotates further, and the tip portion 162A of the first arm 162 of the lever 160 reaches the second cam portion 153B. Contact. The lever 160 swings when the first arm 162 is pushed by the second cam portion 153B, and the hook 163A is disengaged from the claw portion 121C of the sun gear 121 and positioned at the detached position. Since the rotation of the sun gear 121 of the clutch 120 cannot be stopped by the lever 160, when the input gear 122B is rotated, the output gear 123B is in a disengaged state in which the driving force is not transmitted. As a result, the driving force from the motor 3 cannot be transmitted to the developing roller 61, and even if the motor 3 rotates, the sun gear 121 only idles and the developing roller 61 does not rotate.

When the developing roller 61 is maintained at the separated position, the cam 150 stops at the position where the lever 160 is at the disengaged position as shown in FIGS. 14(a) and 14(b). Of the four cams 150, when the yellow cam 150Y is to be temporarily stopped while the developing roller 61 is at the separated position, it is further rotated from the state of FIGS. 14(a) and 14(b). Then, as shown in FIGS. 15A and 15B, the contact portion 172 is positioned at the end of the second holding surface F2 on the second guide surface F4 side (immediately before the contact portion 172 contacts the second guide surface F4). position).

When moving the developing roller 61 from the separated position to the contact position, the cam 150 is rotated from the state shown in FIGS. 14(a) and 14(b) or FIGS. Then, the contact portion 172 slides on the second guide surface F4 and is positioned to face the first holding surface F1 as shown in FIG. As a result, the slide shaft portion 171 moves in the rotation axis direction due to the biasing force of the spring 173 and is separated from the slide member 64 . The slide member 64 returns to the position shown in FIG. 4A, and the developing cartridge 60 returns to the solid line position shown in FIG. This causes the developing roller 61 to come into contact with the photosensitive drum 50 . The developing roller 61 contacts the photosensitive drum 50 when the contact portion 172 passes through a position of the second guide surface F4 near the second holding surface F2 (see FIG. 15B).

Then, as described above, the lever 160 is positioned at the engaged position where the sun gear 121 is engaged with the circular base portion 153A, so that the clutch 120 is in the transmission state.

In the present embodiment, the image forming apparatus 1 moves the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61Y in accordance with the movement of the sheet S when the toner image is transferred onto the sheet S. The roller 61K is moved to the contact position, and after the toner image is transferred, it is sequentially moved to the separation position. Therefore, the cams 150Y, 150M, and 150C are assembled such that the phase of the first cam portion 152A is shifted by a predetermined angle (see FIG. 8). More precisely, the cams 150M and 150C use the same parts, and the cam 150Y has a longer length in the rotational direction of the first cam portion 152A than the cams 150M and 150C. The phases of the cams 150Y, 150M, and 150C at the downstream end of the first cam portion 152A in the rotational direction are shifted by a predetermined angle, and the cams 150Y and 150M are at the upstream end of the first cam portion 152A in the rotational direction. The phases are aligned.
On the other hand, the cam 150K is the same component as the cams 150M and 150C, and is controlled by the control unit 2 so as to operate with a predetermined angle and phase lag behind the cams 150M and 150C.

The control unit 2 is a device that controls the overall operation of the image forming apparatus 1 . The control unit 2 has a CPU, a ROM, a RAM, an input/output unit, etc., and executes each process by executing a pre-stored program.

In this embodiment, the control unit 2 controls the YMC clutch 140A and the K clutch 140K based on signals from the paper feed sensors 28A, 38A, pre-registration sensors 28B, 48B, post-registration sensors 28C, and separation sensors 4K, 4C. and controls the contact/separation of the developing roller 61 with respect to the photosensitive drum 50 .

In the present embodiment, when the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are at the separated positions, the photosensitive drum 50 adjacent to the upstream side in the moving direction of the sheet S is exposed to a laser beam. Since it overlaps with the optical path of light, the image forming apparatus 1 is configured to be positioned at the contact position before starting the exposure of the adjacent photosensitive drum 50 on the upstream side.

Regarding the second developing roller 61M and the third developing roller 61C, the setting of the length in the rotational direction of the first cam portion 152A of the cams 150Y, 150M, and 150C and the mechanical setting of the mutual phase shift, , is positioned at the contact position before exposure of the photosensitive drum 50 adjacent on the upstream side is started. Specifically, in order to position the second developing roller 61M at the contact position before the exposure of the first developing roller 61Y, the cams 150Y and 150M are moved before the first developing roller 61Y contacts the first photosensitive drum 50Y. The second developing roller 61M is set to contact the second photosensitive drum 50M. That is, t2 is set to satisfy t2≦t1, where t1 is the time at which the first developing roller 61Y is brought into contact with the first photosensitive drum 50Y, and t2 is the time at which the second developing roller 61M is brought into contact with the second photosensitive drum 50M. . More specifically, in the present embodiment, t2=t1 is set.

On the other hand, regarding the fourth developing roller 61K, the controller 2 controls the cam 150K to lag behind the cam 150C by a predetermined angle in relation to the third developing roller 61C during color printing. That is, the control section 2 starts exposing the third photosensitive drum 50C when performing color printing using the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K. First, the third developing roller 61C is moved to the contact position and the fourth developing roller 61K is moved to the contact position. After the development of the third photosensitive drum 50C is completed and before the development of the fourth photosensitive drum 50K is completed, the third developing roller 61C is moved to the separated position. After the development of the fourth photosensitive drum 50K is completed, the fourth developing roller 61K is moved to the separated position.

On the other hand, when forming an image on the sheet S using only the fourth developing roller 61K, the control unit 2 maintains the first developing roller 61Y, the second developing roller 61M, and the third developing roller 61C at the separated positions, Before starting the exposure of the fourth photosensitive drum 50K, the fourth developing roller 61K is moved to the contact position. After the development of the fourth photosensitive drum 50K is completed, the fourth developing roller 61K is moved to the separated position.

In addition, the control unit 2 performs control to match the timing of conveying the sheet S with the contact timing of the yellow first developing roller 61Y on the most upstream side with the first photosensitive drum 50Y. That is, the control unit 2 rotates the cams 150Y, 150M, and 150C during a period after the start of conveying the sheet S and before the sheet S reaches the first photosensitive drum 50Y. Then, the first development roller 61Y comes into contact with the first photosensitive drum 50Y at the temporary stop timing after the first time T1 has elapsed from the time when the ON signal is no longer acquired from the separation sensor 4C (the time when the OFF signal is obtained). The YMC clutch 140A is controlled to stop the cams 150Y, 150M, and 150C at the temporary stop timing. Then, the YMC clutch 140A is controlled to rotate the cams 150Y, 150M, and 150C at the restart timing after the second time T2 has elapsed since the pre-registration sensor 28B detected the passage of the front end of the sheet S, thereby rotating the first developing roller 61Y. is brought into contact with the first photosensitive drum 50Y to form an image.

Further, in the present embodiment, when the controller 2 continuously forms images on a plurality of sheets S, the post-registration sensor 28C detects the trailing edge of the previous sheet (hereinafter referred to as "first sheet") S. , the next sheet (hereinafter referred to as "second sheet") S has not yet been supplied from the trays 21, 31, and 41 and has not been conveyed. In this case, a predetermined waiting time Tw is set. Further, in this case, the control unit 2 controls the YMC clutch 140A and/or the K clutch 140K to rotate the cam 150 after the development of the image transferred to the first sheet S is completed, thereby rotating the developing roller 61. Move from the contact position to the separation position. The predetermined time here is a fourth time T4 described later in the case of color printing, and a fourth time T24 described later in the case of monochrome printing. In addition, 0 may be sufficient as predetermined time. That is, if the second sheet S is not being conveyed when the post-registration sensor 28C detects the passage of the trailing edge of the first sheet S, the control unit 2 sets the waiting time Tw and also sets the waiting time Tw. The developing roller 61 may be moved from the contact position to the separated position after the development of the image transferred to S is completed.

Further, the control section 2 is controlled when the image data of the image to be transferred to the second sheet S is ready and when the standby time Tw has passed after the predetermined time (fourth time T4 or T24) has passed. Then, the feeding mechanism 22 is controlled to start feeding the second sheet S from the first tray 21 , the second tray 31 or the manual feed tray 41 toward the photosensitive drum 50 . After that, the control unit 2 controls the YMC clutch 140A and/or the K clutch 140K according to the conveyance of the second sheet S to rotate the cam 150, thereby moving the developing roller 61 from the separated position to the contact position. Let Note that when the image data of the image to be transferred to the sheet S is ready, it means when the image data included in the print job received by the image forming apparatus 1 has been developed into raster format image data. be.

The standby time Tw is equal to or longer than the time obtained by subtracting the second arrival time from the first arrival time, which will be described later. The first arrival time is the time from when the developing roller 61 (the first developing roller 61Y for color printing, the fourth developing roller 61K for monochrome printing) starts to separate from the corresponding photosensitive drum 50, and the developing roller 61 is After separating from the photosensitive drum 50, the developing roller 61 contacts the photosensitive drum 50 again, and the development start position on the surface of the photosensitive drum 50 transfers the toner image to the second sheet S. is the time to reach the transfer position between . The second arrival time is the time from when the second sheet S starts to be fed from the sheet tray to when the leading edge of the image forming area of the second sheet S reaches the transfer position. The image forming area is an area on the surface of the sheet S where an image is actually formed (a toner image is transferred).

In the present embodiment, the controller 2 increases the standby time Tw for a sheet tray having a shorter distance along the conveying path of the sheet S from the photosensitive drum 50Y. In other words, the controller 2 reduces the standby time Tw for a sheet tray that is located at a greater distance along the transport path of the sheet S from the photosensitive drum 50Y. Specifically, as shown in FIG. 26, the controller 2 sets the standby time Tw of the first tray 21 from the first arrival time TA1 to the time when the second sheet S starts to be supplied from the first tray 21. A first standby time TwM is set by subtracting a second arrival time TA2 until the leading edge of the image forming area of the second sheet S reaches the transfer position.

Further, the controller 2 sets the waiting time Tw of the manual feed tray 41, which is shorter than the first tray 21 along the conveying path of the sheet S from the photosensitive drum 50Y, to a second waiting time TwM longer than the first waiting time TwM. Set the waiting time TwL. Specifically, as shown in FIG. 27, the controller 2 sets the standby time Tw of the manual feed tray 41 to the second time from the time when the second sheet S starts to be fed from the manual feed tray 41 from the first arrival time TA1. A second standby time TwL is set by subtracting the second arrival time TA4 until the leading edge of the image forming area of the sheet S reaches the transfer position.

Further, the control unit 2 sets the waiting time Tw of the second tray 31 longer than the first tray 21 along the conveying path of the sheet S from the photosensitive drum 50Y to a third waiting time TwM shorter than the first waiting time TwM. is set to the waiting time TwS. Specifically, as shown in FIG. 28, the controller 2 sets the standby time Tw of the second tray 31 from the first arrival time TA1 to the time when the second sheet S starts to be supplied from the second tray 31. A third standby time TwS is set by subtracting the second arrival time TA3 until the leading edge of the image forming area of the second sheet S reaches the transfer position.

In this embodiment, the standby times TwL, TwM, and TwSj are set in advance and stored in the ROM of the control unit 2 or the like. Note that the second arrival time is long for a sheet tray having a large distance along the sheet conveying path from the photosensitive drum, so the value obtained by subtracting the second arrival time from the first arrival time may be 0 or less. be. In this case, the waiting time should be set to 0.

After setting the standby time Tw, the controller 2 counts down the standby time Tw every several milliseconds. Note that the countdown of the standby time Tw may be started immediately after the standby time Tw is set, or the developing roller 61 (in the case of color printing) after the development of the image transferred to the first sheet S is completed. may be started after the movement of the first developing roller 61Y (or the fourth developing roller 61K in the case of monochrome printing) from the contact position to the separated position is completed.

Further, in the present embodiment, in addition to the first condition that the image data of the image to be transferred to the sheet S is ready, the control unit 2 also determines that the warm-up operation such as preheating of the fixing device 80 is completed. The second condition is that the image forming apparatus 1 is ready to perform image formation, and the third condition is that the timing does not interfere with the previous sheet S even if the next sheet S is supplied. If it is satisfied, it is determined whether or not the waiting time Tw has passed. A case where the third condition is satisfied is a case where a predetermined time has elapsed from the point in time when the previous sheet S was supplied such that even if the next sheet S is supplied, it does not interfere with the previous sheet S ( This includes the case where the sheet S does not exist within the main housing 10).

Further, the control unit 2 controls the sheet interval, which is the interval between the trailing edge of the first sheet S and the leading edge of the second sheet S in the conveying direction of the sheet S, to the sheet feed sensors 28A and 38A, the pre-registration sensor 28B, and the like. 48B, calculated and acquired based on the signal from the post-registration sensor 28C. Then, the controller 2 determines that the second sheet S has already been fed when a predetermined time (fourth time T4 or T24) has passed since the post-registration sensor 28C detected the passage of the trailing edge of the first sheet S. When it is determined that the sheet interval is larger than the predetermined interval, the YMC clutch 140A and/or the K clutch 140A and/or the K clutch 140A and/or the K clutch 140A and/or the K clutch 140A after the image transferred to the first sheet S is completed. By controlling 140K to rotate the cam 150, the developing roller 61 is moved from the contact position to the separated position.

After that, the control unit 2 controls the YMC clutch 140A and/or the K clutch 140K according to the conveyance of the second sheet S to rotate the cam 150, thereby moving the developing roller 61 from the separated position to the contact position. Specifically, after separating the developing roller 61 from the photosensitive drum 50 , the control unit 2 rotates and temporarily stops the cam 150 to match the timing of conveying the second sheet S and the contact timing of the developing roller 61 . Then, after the pre-registration sensor 28B detects the passage of the front end of the second sheet S, the cam 150 is rotated at the restart timing to bring the developing roller 61 into contact with the photosensitive drum 50 .

On the other hand, the controller 2 stops the second sheet S from being conveyed when a predetermined time (fourth time T4 or T24) has passed since the post-registration sensor 28C detected the passage of the trailing edge of the first sheet S. When it is determined that the sheet interval is equal to or less than the predetermined interval, the cam 150 is not rotated, and the image transferred to the second sheet S is developed while the developing roller 61 is positioned at the contact position. conduct.

In the case of color printing, the predetermined interval is the time difference between the time at which the pre-registration sensors 28B and 48B detect the passage of the trailing edge of the first sheet S and the time at which the passage of the leading edge of the second sheet S is detected. The sheet interval is set to be longer than the time required for the first developing roller 61Y to move from the contact position to the separated position to the contact position in this order during one rotation of 150Y. In the case of monochrome printing, the predetermined interval is the time difference between the time at which the post-registration sensor 28C detects the passage of the trailing edge of the first sheet S and the time at which the passage of the leading edge of the second sheet S is detected by the cam 150K. The sheet interval is set such that the time required for the fourth developing roller 61K to move in the order of the contact position, the separation position, and the contact position is longer than the time required for the fourth developing roller 61K to rotate once. The sheet interval less than the predetermined interval is such a small sheet interval that once the developing roller 61 is separated, the developing roller 61 cannot be brought into contact with the photosensitive drum 50 in time for the start of development of the photosensitive drum 50.例文帳に追加

Next, an example of processing of the control unit 2 will be described. The control unit 2 concurrently executes the contact/separation processing of the developing roller 61 shown in FIG. 16 and the sheet supply processing shown in FIG.
As shown in FIG. 16, when the control unit 2 receives a print job, the waiting time (second waiting time) TwL of the manual feed tray 41, the waiting time (first waiting time) TwM of the first tray 21, and The waiting time (third waiting time) TwS of the second tray 31 is read from the ROM or the like and set (S11). After setting the waiting times TwL, TwM, and TwS, the control unit 2 counts down the waiting times TwL, TwM, and TwS every 1 ms, for example.

Further, as shown in FIG. 17, after receiving the print job, the control unit 2 determines whether or not the image data of the image to be transferred to the sheet S is ready (S31). If the image data is ready (S31, Yes), the control unit 2 determines based on information on the sheet tray from which the sheets S included in the print job are supplied, information on the size of the sheets S included in the print job, and the like. It is determined whether the supply source is the manual feed tray 41 or not, based on the information of the sheet tray of the supply source.

If the supply source is not the manual feed tray 41 (S32, No), the controller 2 determines whether the supply source is the second tray 31 (S33). If the source of supply is not the second tray 31 (S33, No), the source of supply is the first tray 21. Therefore, the controller 2 determines whether the first waiting time TwM has become 0 as a result of the countdown. is determined (S34). When the first waiting time TwM becomes 0 (S34, Yes), the control unit 2 drives the paper feed roller 23 to pick up the sheet S from the first tray 21 and start conveying the sheet S ( S35).

If the supply source is the manual feed tray 41 in step S32 (S32, Yes), the control unit 2 determines whether or not the second waiting time TwL has become 0 (S36). (S36, Yes), the paper feed roller 43 is driven to pick up the sheet S from the manual feed tray 41, and transport of the sheet S is started (S37). Further, when the supply source is the second tray 31 in step S33 (S33, Yes), the control unit 2 determines whether or not the third waiting time TwS has become 0 (S38). In the case (S38, Yes), the paper feed roller 33 is driven to pick up the sheet S from the second tray 31 and start conveying the sheet S (S39).

After picking up the sheet S, the control unit 2 determines whether or not there is a next page to be printed (S40), and if there is a next page (S40, Yes), repeats the processing from step S31 If there is no next page (S40, No), the sheet feeding process is terminated.

Returning to FIG. 16, after setting the standby time Tw in step S11, the control unit 2 executes contact control processing to bring the developing roller 61 into contact with the photosensitive drum 50 (S12). After that, the control unit 2 controls the control unit 2 to set the trailing edge of the conveyed sheet S to pass the post-registration sensor 28C and turn off the post-registration sensor for a predetermined time (fourth time T4 in the case of color printing, and T4 in the case of monochrome printing). or the fourth time T24) has elapsed (S13). If a predetermined time has passed since the sensor was turned off after registration (S13, Yes), the control unit 2 determines whether or not there is a next page (S14). Then, for example, when printing on one sheet S, there is no next page (S14, No). (S15), and when the separation control ends, the contact separation processing ends.

Here, the details of the contact control process and the separation control process will be described by taking the case of printing on one sheet S as an example.
First, with reference to the flow chart of FIG. 18 and the timing chart of FIG. 19, the case of color printing in which the image to be formed is a color image will be described. In FIG. 19, the timing chart of the operation of the uppermost yellow first developing roller 61Y is superimposed on the second developing roller 61M, the third developing roller 61C and the third developing roller 61C of magenta, cyan and black with different line types. 4 shows the operation of the developing roller 61K.

When processing color printing, all the developing rollers 61 are at the separated position before the image forming operation. When starting the contact control process shown in FIG. 18(a), the control unit 2 first turns on the YMC clutch 140A (S201, t0) and then turns on the K clutch in order to sequentially bring the developing roller 61 to the contact position. 140K is turned ON (S202, t0). As a result, the cams 150Y, 150M, 150C and 150K rotate. As soon as the cams 150Y, 150M, 150C and 150K rotate, the separation sensors 4C and 4K are turned off (t31).

After picking up the sheet S from the first tray 21 and starting to convey the sheet S (FIG. 17, S35, t51), the control unit 2, for example, picks up the sheet S before the sheet S reaches the first photosensitive drum 50Y. During the period, it is determined whether or not the first time T1 has passed since the separation sensor 4C for cyan outputs the OFF signal (S210). When the control unit 2 determines that the first time T1 has passed (S210, Yes), it turns off the YMC clutch 140A (S211, t32), and stops the cams 150Y, 150M, 150C at the temporary stop timing. The first time T1 is set to a time such that the contact portion 172 of the yellow cam follower 170 is positioned closest to the second guide surface F4 of the second holding surface F2 of the cam 150Y at the temporary stop timing. It is As a result, when the rotation of the cams 150Y, 150M, and 150C resumes, the yellow cam follower 170 immediately moves to the second guide surface F4, and the first developing roller 61Y starts moving toward the contact position.

Next, the control unit 2 determines whether or not the second time T2 has passed since the pre-registration sensor ON (t53, when the leading edge of the sheet S passes the pre-registration sensor 28B) (S212), and determines that it has passed. Then (S212, Yes), the YMC clutch 140A is turned ON (S213, t33), and the rotation of the cams 150Y, 150M, 150C is restarted at the restart timing. The second time T2 is set so that the development of the first photosensitive drum 50Y by the first developing roller 61Y can be completed in time for the transfer of the toner image onto the conveyed sheet S. As shown in FIG.

Further, the control unit 2 determines that the first time T21 has elapsed since the separation sensor 4K for black outputs an OFF signal during a period after the start of conveying the sheet S and before the sheet S reaches the fourth photosensitive drum 50K. It is determined whether or not (S220). When the control unit 2 determines that the first time T21 has passed (S220, Yes), it turns off the K clutch 140K (S221, t42), and stops the cam 150K at the temporary stop timing. This first time T21 is set to a time such that the contact portion 172 of the black cam follower 170 is positioned closest to the second guide surface F4 of the second holding surface F2 of the cam 150K at the temporary stop timing. It is As a result, when the rotation of the cam 150K resumes, the cam follower 170 immediately moves to the second guide surface F4, and the fourth developing roller 61K starts moving toward the contact position. Note that the first time T21 and the first time T1 are different times.

Next, the control unit 2 determines whether or not the third time T3 has elapsed since the YMC clutch 140A was turned ON (t33) at the restart timing (S222). Clutch 140A is turned OFF (S223, t36) to stop cams 150Y, 150M and 150C. This third time T3 is set to a time during which all of the first developing roller 61Y, the second developing roller 61M and the third developing roller 61C are positioned at the contact position.

Next, the control unit 2 determines whether a second time T22 has elapsed since the post-registration sensor ON (t54, when the leading edge of the sheet S passes the post-registration sensor 28C) (S224). (S224, Yes), K clutch 140K is turned ON (S225, t43), and cam 150K is rotated. The second time T22 is set so that the development of the fourth photosensitive drum 50K by the fourth developing roller 61K can be completed in time for the toner image to be transferred onto the sheet S that has been conveyed. As a result, the timing at which the fourth developing roller 61K is positioned at the contact position is just before the exposure of the third photosensitive drum 50C is started.

Next, the control unit 2 determines whether or not the third time T23 has elapsed since the K clutch 140K was turned ON (t43) (S226). It is turned OFF (S227, t44) to stop the cam 150K and terminate the contact control process. The third time T23 is set such that the fourth developing roller 61K is positioned at the contact position.

When printing on one sheet S, there is no next page (FIG. 16, S14, No), so the control section 2 executes separation control processing (S15). Specifically, as shown in FIG. 18B, the control unit 2 determines whether the fourth time T4 has elapsed since the post-registration sensor was turned off (t57) (S230), and if it determines that it has elapsed (S230 , Yes), the YMC clutch 140A is turned ON (S231, t37), the cams 150Y, 150M and 150C are rotated to start separating the first developing roller 61Y, the second developing roller 61M and the third developing roller 61C sequentially. At the fourth time T4, the development of the first photosensitive drum 50Y by the first developing roller 61Y is completed, and immediately after the transfer from the first photosensitive drum 50Y to the sheet S is completed, the first developing roller 61Y moves to the separated position. The time is set to allow movement.

Next, the control unit 2 determines whether or not the fourth time T24 has elapsed since the post-registration sensor was turned off (t57) (S232). S233, t45), the cam 150K is rotated. At the fourth time T24, development is completed on the fourth photosensitive drum 50K by the fourth developing roller 61K, and immediately after the transfer from the fourth photosensitive drum 50K to the sheet S is completed, the fourth developing roller 61K moves to the separated position. The time is set to allow movement.

Next, the controller 2 determines whether or not the separation sensor 4C for cyan has output an ON signal (separation signal) (S240). is turned off (S241, t40) to stop the cams 150Y, 150M and 150C.

Next, the control unit 2 determines whether or not the separation sensor 4K for black has output an ON signal (S242). (S243, t46), the cam 150K is stopped, and the separation control process ends.

In this manner, the developing rollers 61 are sequentially moved from the separated position to the contact position during printing of one sheet, and further moved from the contact position to the separated position after printing. Specifically, as shown in FIG. 20, the image forming apparatus 1 brings the first developing roller 61Y into contact with the first photosensitive drum 50Y at time t1, and brings the second developing roller 61M into contact with the second photosensitive drum 50M at time t2. , the third developing roller 61C is brought into contact with the third photosensitive drum 50C at time t3, and the fourth developing roller 61K is brought into contact with the fourth photosensitive drum 50K at time t4. In this embodiment, time t1=t2. Also, t1<t3, t2<t3, and t3<t4. Therefore, in the present embodiment, |t1-t2| is the time between time t1 and t2, and |t2-t3| is the time between time t2 and t3, and |t1-t2|<|t2-t3 | In the present invention, the later time is assumed to have a greater value than the previous time, the value obtained by subtracting the previous time from the later time is positive, and the value obtained by subtracting the subsequent time from the previous time is negative. and And the absolute value of the value obtained by subtracting the time and the time means the length of time. Since the relationship between t1 and t2 may be t2<t1, t2-t1 is a negative value in this case. Although it is not necessary that t2<t1, in this case the second developing roller 61M is moved to the contact position earlier.

Further, the image forming apparatus 1 separates the first developing roller 61Y from the first photosensitive drum 50Y at time t11, separates the second developing roller 61M from the second photosensitive drum 50M at time t12, and separates the third developing roller 61M from the second photosensitive drum 50M at time t13. The developing roller 61C is separated from the third photosensitive drum 50C, and at time t14, the fourth developing roller 61K is separated from the fourth photosensitive drum 50K. In this embodiment, t11<t12<t13<t14. Therefore, |t1-t2| is the time between times t1 and t2, and |t11-t12| is the time between times t11 and t12, and |t1-t2|<|t11-t12| is satisfied.

Next, with reference to the flow chart of FIG. 21 and the timing chart of FIG. 22, a case where the image to be formed on one sheet S is monochrome printing will be described.

When processing monochrome printing, all the developing rollers 61 are at the separated position before the image forming operation. During monochrome printing, the control unit 2 does not move the YMC clutch 140A at all, and keeps the first developing roller 61Y, the second developing roller 61M, and the third developing roller 61C positioned at the separated positions. On the other hand, when starting the contact control process shown in FIG. 21(a), the control section 2 first turns ON the K clutch 140K in order to bring the fourth developing roller 61K to the contact position (S301, t0). This causes the cam 150K to rotate. As soon as the cam 150K rotates, the separation sensor 4K for black turns OFF (t61).

Then, for example, after picking up the sheet S from the first tray 21 and starting to convey the sheet S (FIG. 17, S35, t51), the control unit 2 controls the control unit 2 before the sheet S reaches the fourth photosensitive drum 50K. During the period, it is determined whether or not the first time T21 has passed since the separation sensor 4K for black outputs an OFF signal (S310). When the control unit 2 determines that the first time T21 has passed (S310, Yes), it turns off the K clutch 140K (S311, t62), and stops the cam 150K at the temporary stop timing. This first time T21 is set to a time such that the contact portion 172 of the black cam follower 170 is positioned closest to the second guide surface F4 of the second holding surface F2 of the cam 150K at the temporary stop timing. It is As a result, when the rotation of the cam 150K resumes, the cam follower 170 immediately moves to the second guide surface F4, and the fourth developing roller 61K starts moving toward the contact position. Note that the first time T21 in monochrome printing and the first time T1 in color printing are different times.

Next, the control unit 2 determines whether or not the second time T22 has elapsed since the post-registration sensor was turned on (t54) (S312). (S313, t63) At the restart timing, the rotation of the cam 150K is restarted. The second time T22 is set so that the development of the fourth photosensitive drum 50K by the fourth developing roller 61K can be completed in time for the toner image to be transferred onto the sheet S that has been conveyed. Note that the second time T22 in monochrome printing and the second time T2 in color printing are different times.

Next, the control unit 2 determines whether or not the third time T23 has passed since the K clutch 140K was turned ON (t63) (S324). It is turned OFF (S325, t66) to stop the cam 150K and terminate the contact control process. The third time T23 is set such that the fourth developing roller 61K is positioned at the contact position.

When printing on one sheet S, there is no next page (FIG. 16, S14, No), so the control section 2 executes separation control processing (S15). Specifically, as shown in FIG. 21B, the control unit 2 determines whether the fourth time T24 has elapsed since the post-registration sensor was turned off (t57) (S332), and if it determines that it has elapsed (S332 , Yes), the K clutch 140K is turned ON (S333, t67), and the cam 150K is rotated.

Next, the control unit 2 determines whether or not the separation sensor 4K for black has output an ON signal (S342). (S343, t70), the cam 150K is stopped, and the separation control process ends.

In this manner, the fourth developing roller 61K moves from the separated position to the contact position when printing one sheet, and then moves from the contact position to the separated position after printing. At this time, since the first developing roller 61Y, the second developing roller 61M, and the third developing roller 61C remain positioned at the separated position, the first developing roller 61Y, the second developing roller 61M, and the third developing roller 61Y are kept at the separated positions. There is no useless rotation of 61C.

As shown in FIGS. 23 to 25, the image forming apparatus 1 performs color printing using the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K. When the toner image is transferred to S, the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are moved to the contact positions in accordance with the movement of the sheet S, and the respective photosensitive drums are moved. After the development of 50 is completed, it is moved to the separated position.

Specifically, as shown in FIG. 23A, before the sheet S reaches the most upstream first photosensitive drum 50Y, the first developing roller 61Y, the second developing roller 61M, and the third developing roller 61C are rotated. and the fourth developing roller 61K are all positioned at the separated position. When the developing rollers 61 are at the separated position, the second developing cartridge 60M overlaps the optical path of the laser beam for exposing the first photosensitive drum 50Y, and the third developing cartridge 60C is for the laser beam for exposing the second photosensitive drum 50M. , and the fourth developing cartridge 60K overlaps the optical path of the laser beam that exposes the third photosensitive drum 50C.

Then, as shown in FIG. 23B, when the sheet S approaches the first photosensitive drum 50Y, the image forming apparatus 1 performs the first developing cartridge 60Y and the first developing cartridge 60Y before starting the exposure of the first photosensitive drum 50Y. The two developing cartridges 60M are simultaneously moved to move the first developing roller 61Y and the second developing roller 61M to the contact position. As a result, the laser light for exposing the first photosensitive drum 50Y does not overlap the second developing cartridge 60M, and the first photosensitive drum 50Y can be exposed. The first developing roller 61Y develops the first photosensitive drum 50Y, and the toner image is transferred onto the sheet S from the first photosensitive drum 50Y.

Then, as shown in FIG. 23C, when the sheet S approaches the second photosensitive drum 50M, the image forming apparatus 1 moves the third developing cartridge 60C before starting the exposure of the second photosensitive drum 50M. , moves the third developing roller 61C to the contact position. As a result, the laser light for exposing the second photosensitive drum 50M does not overlap the third developing cartridge 60C, and the second photosensitive drum 50M can be exposed. The second developing roller 61M develops the second photosensitive drum 50M, and the toner image is transferred onto the sheet S from the second photosensitive drum 50M.

Then, as shown in FIG. 23D, when the sheet S approaches the third photosensitive drum 50C, the image forming apparatus 1 moves the fourth developing cartridge 60K before starting the exposure of the third photosensitive drum 50C. , the fourth developing roller 61K is moved to the contact position. As a result, the laser light for exposing the third photosensitive drum 50C does not overlap the fourth developing cartridge 60K, and the third photosensitive drum 50C can be exposed. The third developing roller 61C develops the third photosensitive drum 50C, and the toner image is transferred onto the sheet S from the third photosensitive drum 50C. Further, since the fourth developing roller 61K is positioned at the contact position, the fourth developing roller 61K can develop the fourth photosensitive drum 50K.

Then, as shown in FIG. 24A, after the development of the first photosensitive drum 50Y by the first developing roller 61Y is completed, the image forming apparatus 1 performs the development of the second photosensitive drum 50M by the second developing roller 61M. Before the development is completed, the first developing cartridge 60Y is moved to move the first developing roller 61Y to the separated position.

Then, as shown in FIG. 24B, the image forming apparatus 1 moves the third photosensitive drum 50C by the third developing roller 61C after the development of the second photosensitive drum 50M by the second developing roller 61M is completed. Before the development is completed, the second developing cartridge 60M is moved to move the second developing roller 61M to the separated position.

Then, as shown in FIG. 24C, the image forming apparatus 1 moves the fourth photosensitive drum 50K by the fourth developing roller 61K after the development of the third photosensitive drum 50C by the third developing roller 61C is completed. Before the development is completed, the third developing cartridge 60C is moved to move the third developing roller 61C to the separated position.

Then, as shown in FIG. 24D, after the development of the fourth photosensitive drum 50K by the fourth developing roller 61K is completed, the image forming apparatus 1 moves the fourth developing cartridge 60K to move the fourth developing roller 61K. Move to the separated position.

On the other hand, when the image forming apparatus 1 performs monochrome printing using only the fourth developing roller 61K as shown in FIGS. , the first developing roller 61Y, the second developing roller 61M, and the third developing roller 61C for colors other than black among the fourth colors are maintained at the separated positions. As the sheet S moves, the fourth developing roller 61K corresponding to black is moved to the contact position, and after the development of the fourth photosensitive drum 50K is completed, it is moved to the separated position.

Specifically, as shown in FIG. 25B, the image forming apparatus 1 moves the fourth developing cartridge 60K to move the fourth developing roller 61K to the contact position before starting the exposure of the fourth photosensitive drum 50K. move to Then, as shown in FIG. 25C, after the development of the fourth photosensitive drum 50K is completed, the fourth developing roller 61K is moved to the separated position.

Next, with reference to the flowcharts of FIGS. 16 and 17 and the timing charts of FIGS. 26 to 28, the process of printing a plurality of sheets S continuously will be described, taking the case of color printing as an example. do.

First, the case of supplying the next sheet (second sheet) S from the first tray 21 will be described with reference to the timing chart of FIG.
When printing on a plurality of sheets S continuously, the trailing edge of the preceding sheet (first sheet) S passes the post-registration sensor 28C in step S13 of FIG. When four hours T4 (predetermined time) have passed (S13, Yes) and there is a next page (S14, Yes), the control unit 2 determines whether the second sheet S has already been picked up and is being conveyed. is determined (S16).

If the second sheet S has not yet been picked up and is not being conveyed (S16, No), the control unit 2 sets waiting times TwL, TwM, and TwS (S17) and starts counting down. After the development of the image transferred to the sheet S is completed, the YMC clutch 140A is turned ON to start rotating the cams 150Y, 150M, and 150C, and execute separation control processing (S20, t37) (see FIG. 18B). ). The waiting time Tw set in step S17 may be the same as or different from the waiting time Tw of the first sheet S set in step S11.

Further, even if the image data of the image to be transferred to the second sheet S is ready at (t37) when the fourth time T4 has elapsed since the post-registration sensor was turned off (Fig. 17, S31, Yes), the supply of the second sheet S from the first tray 21 is waited until the first waiting time TwM elapses. Then, when the first waiting time TwM becomes 0 (S34, Yes), the controller 2 drives the paper feed roller 23 to pick up the second sheet S from the first tray 21, and the second sheet S is started (S35, t71).

After completing the process of sequentially separating the developing rollers 61Y, 61M, 61C from the corresponding photosensitive drums 50Y, 50M, 50C, the control unit 2 brings the developing rollers 61Y, 61M, 61C into contact with the corresponding photosensitive drums 50Y, 50M, 50C. 16, S12). Specifically, the controller 2 continues to rotate the cams 150Y, 150M, and 150C even after the time point (t40) when the cyan distance sensor 4C outputs the ON signal, and the time when the cyan distance sensor 4C outputs the OFF signal. After the first time T1 has elapsed from (t41), the YMC clutch 140A is turned OFF to temporarily stop the cams 150Y, 150M, and 150C (t38).

After that, when the leading edge of the second sheet S conveyed from the first tray 21 passes the pre-registration sensor 28B (t73), the controller 2 turns on the YMC clutch 140A when the second time T2 elapses. The rotation of 150Y, 150M, and 150C is resumed (t39), and the image transferred to the second sheet S is developed while the developing roller 61 is brought into contact with the corresponding photosensitive drum 50 in sequence. After that, the control unit 2 executes the processes after step S13 in FIG. 16 .

In the present embodiment, separation control and contact control can be performed separately for the developing rollers 61Y, 61M, 61C and the fourth developing roller 61K. The cams 150Y, 150M, and 150C continue to rotate even after the separation sensor 4C outputs the ON signal, and contact control can be started without waiting for the cam 150K to stop. When the separation sensor 4C for cyan outputs an ON signal at time t40, the YMC clutch 140A is turned OFF to temporarily stop the cams 150Y, 150M and 150C. 150M and 150C may be rotated.

In the first tray 21, starting the supply of the second sheet S when the first waiting time TwM has passed from the time (t37) when the fourth time T4 has passed since the post-registration sensor was turned off (t57) ( t71), the timing at which the leading edge of the image forming area of the second sheet S reaches the transfer position (t75, when the second arrival time TA2 has passed from time t71), and the first developing roller 61Y from the first photosensitive drum 50Y After starting to separate (t37), the timing at which the development start position of the surface of the first photosensitive drum 50Y by the first developing roller 61Y in contact with the first photosensitive drum 50Y again reaches the transfer position (first arrival from time t37). when the time TA1 has elapsed) can be combined.

Next, the case of feeding the second sheet S from the manual feed tray 41 will be described with reference to the timing chart of FIG.
The control unit 2 controls the image data of the image to be transferred to the second sheet S when the fourth time T4 has elapsed after the post-registration sensor 28C was turned OFF (t37) when the trailing edge of the first sheet S passed the post-registration sensor 28C. is ready, the supply of the second sheet S from the manual feed tray 41 is waited until the second waiting time TwL elapses. Then, when the second waiting time TwL becomes 0, the control unit 2 drives the paper feed roller 43 to pick up the second sheet S from the manual feed tray 41 and start conveying the second sheet S ( t81).

After that, the control unit 2 turns on the YMC clutch 140A at the timing when the second time T2 has passed since the leading edge of the second sheet S conveyed from the manual feed tray 41 passed the pre-registration sensor 48B (t83). The cams 150Y, 150M, and 150C are rotated (t39), and the image transferred to the second sheet S is developed while the developing roller 61 is brought into contact with the corresponding photosensitive drum 50 in sequence.

In the manual feed tray 41, when the second waiting time TwL elapses from the time (t37) when the fourth time T4 elapses after the post-registration sensor is turned off (t57), the supply of the second sheet S is started (t81 ), the timing at which the leading edge of the image forming area of the second sheet S reaches the transfer position (t75, when the second arrival time TA4 has passed from time t81), and the separation of the first developing roller 61Y from the first photosensitive drum 50Y. (t37), the timing at which the development start position on the surface of the first photosensitive drum 50Y by the first developing roller 61Y in contact with the first photosensitive drum 50Y again reaches the transfer position (first arrival time from time t37). when TA1 has elapsed) can be combined. Since the manual feed tray 41 has a smaller distance along the conveying path of the sheet S from the first photosensitive drum 50Y than the first tray 21, the second arrival time TA4 is the second arrival time TA2 of the first tray 21 (Fig. 26). Therefore, the second waiting time TwL is set to be longer than the first waiting time TwM.

Next, the case of supplying the second sheet S from the second tray 31 will be described with reference to the timing chart of FIG. 28 .
The control unit 2 controls the image data of the image to be transferred to the second sheet S when the fourth time T4 has elapsed after the post-registration sensor 28C was turned OFF (t37) when the trailing edge of the first sheet S passed the post-registration sensor 28C. is ready, the supply of the second sheet S from the second tray 31 waits until the third waiting time TwS elapses. Then, when the third waiting time TwS becomes 0, the control unit 2 drives the paper feed roller 33 to pick up the second sheet S from the second tray 31 and start conveying the second sheet S. (t91).

After that, the control unit 2 turns on the YMC clutch 140A at the timing when the second time T2 has passed since the leading edge of the second sheet S conveyed from the second tray 31 passed the pre-registration sensor 28B (t93). Then, the cams 150Y, 150M, and 150C are rotated (t39), and the image transferred to the second sheet S is developed while the developing roller 61 is brought into contact with the corresponding photosensitive drum 50 in sequence.

By starting the supply of the second sheet S when the third standby time TwS elapses after the fourth time T4 has elapsed (t37) after the post-registration sensor is turned off (t57) in the second tray 31 ( t91), the timing at which the leading edge of the image forming area of the second sheet S reaches the transfer position (t75, when the second arrival time TA3 has passed from time t91), After starting to separate (t37), the timing at which the development start position of the surface of the first photosensitive drum 50Y by the first developing roller 61Y in contact with the first photosensitive drum 50Y again reaches the transfer position (first arrival from time t37). when the time TA1 has elapsed) can be combined. Since the second tray 31 has a greater distance along the transport path of the sheet S from the first photosensitive drum 50Y than the first tray 21, the second arrival time TA3 is equal to the second arrival time TA2 of the first tray 21 ( 26). Therefore, the third waiting time TwS is set to be shorter than the first waiting time TwM.

Further, as shown in FIG. 16, when the second sheet S is already being conveyed in step S16 (S16, Yes), the control unit 2 acquires the sheet interval between the first sheet S and the second sheet S. (S18), and it is determined whether or not the sheet interval is equal to or less than a predetermined interval (S19). Then, if the sheet interval is not equal to or less than the predetermined interval (S19, No), that is, if the sheet interval is greater than the predetermined interval, the controller 2 separates the first sheet S after the development of the image transferred to the first sheet S is completed. Control processing is executed (S20). After the separation control process is completed, the control unit 2 executes the contact control process (S12), brings the developing roller 61 into contact with the photosensitive drum 50, and develops the image transferred to the second sheet S. , and when the contact control process is completed, the processes after step S13 are executed.

On the other hand, if the sheet interval is smaller than the predetermined interval in step S19 (S19, Yes), the control unit 2 keeps the developing roller 61 positioned at the contact position without separating from the photosensitive drum 50, and develops the image transferred to the Then, when a predetermined time (fourth time T4) has passed since the trailing edge of the second sheet S passed the post-registration sensor 28C and the post-registration sensor was turned OFF (S13, Yes), the controller 2 performs step The processing after S14 is executed.

Effects of the image forming apparatus 1 described above will be described.
After the post-registration sensor 28C detects the passage of the trailing edge of the first sheet S and the post-registration sensor 28C is turned off, the image forming apparatus 1 detects the second sheet when a predetermined time (fourth time T4 or T24) elapses. When the sheet S is not conveyed, the developing roller 61 is separated from the photosensitive drum 50 after the development of the image transferred to the first sheet S is completed, and then the image transferred to the second sheet S is developed. Since the developing roller 61 is brought into contact with the photosensitive drum 50 again to perform the above-mentioned operation, the contact between the developing roller 61 and the photosensitive drum 50 can be suppressed as much as possible.

Since the second sheet S is supplied from the tray 21, 31 or 41 after the waiting time Tw obtained by subtracting the second arrival time from the first arrival time elapses, the development start position on the surface of the photosensitive drum 50 is the transfer position. , the leading edge of the image forming area of the second sheet S can reach the transfer position.

Supplementally, when the distance of the sheet tray from the photosensitive drum 50 (50Y) along the conveying path of the sheet S is small, for example, when the cam 150 is rotated simultaneously with the start of supply of the second sheet S, the photosensitive drum 50 There is a possibility that the leading edge of the image forming area of the second sheet S has already passed the transfer position at the timing when the development start position on the surface of the second sheet S reaches the transfer position. That is, in such a case, there is a possibility that the developing roller 61 cannot be brought into contact with the photosensitive drum 50 in time for the transfer of the leading edge of the image forming area of the second sheet S.

Therefore, by setting the waiting time Tw to the time obtained by subtracting the second arrival time from the first arrival time, the second sheet S can be transferred from the sheet tray having a short distance from the photosensitive drum 50 along the conveying path of the sheet S. Also when supplying, the developing roller 61 can be brought into contact with the photosensitive drum 50 in time for the transfer of the leading edge of the image forming area of the second sheet S. As a result, regardless of the distance from the photosensitive drum 50 along the conveying path of the sheet S of the sheet tray, the developing roller 61 is brought into contact with the photosensitive drum 50 in time for the transfer of the leading edge of the image forming area of the second sheet S. be able to.

Further, the waiting time Tw is set longer for a sheet tray that is located at a shorter distance along the conveying path of the sheet S from the photosensitive drum 50. Therefore, the second sheet S is transferred to the sheet tray at the optimum timing according to the position of each sheet tray. can be supplied toward the photosensitive drum 50.

Further, when the sheet interval between the first sheet S and the second sheet S is larger than the predetermined interval, the developing roller 61 is separated after the development of the image transferred to the first sheet S is completed, and then, Since the developing roller 61 is brought into contact with the conveyance of the second sheet S, contact between the developing roller 61 and the photosensitive drum 50 can be suppressed as much as possible.

Further, the drive transmission mechanism 100 is configured to transmit the driving force to the developing roller 61 when the developing roller 61 is in the contact position, and not to transmit the driving force to the developing roller 61 when the developing roller 61 is in the separated position. Therefore, contact between the developing roller 61 and the photosensitive drum 50 can be suppressed as much as possible. can be suppressed. As a result, deterioration of the toner can be suppressed.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified as appropriate.

For example, in the above embodiment, the sheet interval is calculated based on the signals from the paper feed sensors 28A and 38A, the pre-registration sensors 28B and 48B, and the post-registration sensor 28C, but the present invention is not limited to this. For example, the size of the sheet interval may be determined based on the information indicating which sheet tray is the sheet supply source and the elapsed time after the sheet is picked up.

Further, in the above embodiment, the image forming apparatus 1 has three sheet trays, specifically, the first tray 21, the manual feed tray 41, and the second tray 31 added below the first tray 21. However, a configuration in which the second tray 31 is not provided, that is, a configuration in which only two sheet trays, that is, the first tray 21 and the manual feed tray 41, may be provided. Further, the image forming apparatus may have a configuration in which a third tray having the same configuration as that of the second tray 31 is additionally provided below the second tray 31 . That is, the image forming apparatus may be configured to include four or more sheet trays. Also, the image forming apparatus may be configured to include only one sheet tray. If the distance of the third tray from the photosensitive drum along the sheet conveying path is longer than that of the second tray, the waiting time of the third tray may be zero.

Further, in the above-described embodiment, the third waiting time TwS, which is the waiting time Tw of the second tray 31, was set to a time greater than 0 (see FIG. 28), but the photosensitive drum 50 (50Y) of the second tray 31 ) along the conveying path of the sheet S, the third waiting time TwS may be set to zero.

Further, in the above-described embodiment, the post-registration sensor 28C was exemplified as the sheet sensor, but the sheet sensor may be a pre-registration sensor, a paper feed sensor, or the like.

Further, in the above-described embodiment, the image forming apparatus 1 that prints a color image using toner of four colors was exemplified, but an apparatus that prints a color image using toner of three colors or five colors may be used. . Further, the image forming apparatus may be an apparatus that includes one photosensitive drum, one developing roller, one cam, and the like, and prints a monochrome image using only one color of toner.

Also, the image forming apparatus may be a multifunction machine or a copier.

Reference Signs List 1 image forming apparatus 2 control unit 3 motor 21 first tray 22 supply mechanism 27 registration roller 28B pre-registration sensor 28C post-registration sensor 31 second tray 41 manual feed tray 50 photosensitive drum 50Y first photosensitive drum 50K fourth photosensitive drum 60 development Cartridge 60Y First developing cartridge 60K Fourth developing cartridge 61 Developing roller 61Y First developing roller 61K Fourth developing roller 61X Rotation axis 64 Slide member 90 Support member 100 Drive transmission mechanism 140A YMC clutch 140K K clutch 150 (150Y, 150K) Cam 170 cam follower 182B slope 183B slope S seat

Claims (8)

a photosensitive drum;
a developing cartridge having a developing roller movable between a contact position that contacts the photosensitive drum and a separated position that separates from the photosensitive drum;
a cam rotatable in a predetermined rotational direction for moving the developing roller between the contact position and the separated position , the cam rotating around an axis parallel to the rotational axis of the developing roller; a cam having a first cam portion projecting in the direction of the rotation axis of the developing roller ;
a switching mechanism capable of switching rotation/stop of the cam;
a cam follower that contacts the first cam portion of the cam and slides in the direction of the rotation axis to press the developer cartridge;
at least one sheet tray in which sheets are set;
a supply mechanism for supplying a sheet from the sheet tray toward the photosensitive drum;
a sheet sensor capable of detecting the passage of the sheet on the upstream side of the photosensitive drum in the sheet conveying direction;
a control unit;
When forming an image on a sheet, the control unit
When the sheet sensor detects the passage of the trailing edge of the first sheet and the next second sheet is not conveyed when a predetermined time has passed, the development of the image transferred to the first sheet is completed. afterward, by controlling the switching mechanism to rotate the cam, the developing roller is moved from the contact position to the separated position;
When the image data of the image to be transferred to the second sheet is ready, and when a predetermined waiting time elapses after the elapse of the predetermined time, the feeding mechanism is controlled to remove the second sheet from the sheet tray. The developing roller is moved from the separated position to the contact position by starting to supply the developing roller toward the photosensitive drum and then controlling the switching mechanism to rotate the cam according to the conveyance of the second sheet. An image forming apparatus characterized by: a photosensitive drum;
a developing roller movable between a contact position that contacts the photosensitive drum and a separation position that separates from the photosensitive drum;
a cam that moves the developing roller between the contact position and the separated position and is rotatable in a predetermined rotational direction;
a switching mechanism capable of switching rotation/stop of the cam;
at least one sheet tray in which sheets are set;
a supply mechanism for supplying a sheet from the sheet tray toward the photosensitive drum;
a sheet sensor capable of detecting the passage of the sheet on the upstream side of the photosensitive drum in the sheet conveying direction;
a control unit;
When forming an image on a sheet, the control unit
When the sheet sensor detects the passage of the trailing edge of the first sheet and the next second sheet is not conveyed when a predetermined time has passed, the development of the image transferred to the first sheet is completed. afterward, by controlling the switching mechanism to rotate the cam, the developing roller is moved from the contact position to the separated position;
When the image data of the image to be transferred to the second sheet is ready, and when a predetermined waiting time elapses after the elapse of the predetermined time, the feeding mechanism is controlled to remove the second sheet from the sheet tray. starting to supply the developing roller toward the photosensitive drum, thereafter controlling the switching mechanism according to the conveyance of the second sheet to rotate the cam to move the developing roller from the separated position to the contact position;
The waiting time is
When the developing roller starts to separate from the photosensitive drum, the developing roller separates from the photosensitive drum, and thereafter the developing roller comes into contact with the photosensitive drum again, and the development start position on the surface of the photosensitive drum changes. From the time until reaching the transfer position where the toner image is transferred to the second sheet,
The time obtained by subtracting the time from when the second sheet starts to be fed from the sheet tray to when the leading edge of the image forming area of the second sheet reaches the transfer position. forming device. comprising a plurality of the sheet trays having different distances along the sheet conveying path from the photosensitive drum;
3. The image forming apparatus according to claim 1, wherein the controller increases the standby time for a sheet tray having a shorter distance along the sheet conveying path from the photosensitive drum. When the second sheet is being conveyed when the predetermined time has elapsed since the sheet sensor detected the passage of the trailing edge of the first sheet, the control unit controls the movement of the first sheet in the conveying direction. When it is determined that the sheet interval, which is the interval between the trailing edge and the leading edge of the second sheet, is larger than the predetermined interval, the switching mechanism is controlled after the development of the image transferred to the first sheet is completed. By rotating the cam, the developing roller is moved from the contact position to the separated position. 4. The image forming apparatus according to any one of claims 1 to 3, wherein the image forming apparatus is moved from the separated position to the contact position. The control unit adjusts the sheet interval to the predetermined interval when the second sheet is being conveyed when the predetermined time has elapsed since the sheet sensor detected the passage of the trailing edge of the first sheet. 5. The image to be transferred to the second sheet is developed while the developing roller is positioned at the contact position without rotating the cam when it is determined as follows. Image forming device. a motor;
a driving transmission mechanism for transmitting driving force from the motor to the developing roller,
The cam is mechanically connected to the drive transmission mechanism,
The drive transmission mechanism transmits the driving force from the motor to the developing roller when the developing roller is in the contact position, and transmits the driving force from the motor to the developing roller when the developing roller is in the separated position. 6. The image forming apparatus according to any one of claims 1 to 5, wherein the image forming apparatus is constructed so as not to transmit to the roller. further comprising a support member that supports the developer cartridge;
The developing cartridge has a slide member that is slidable in the rotational axis direction by being pressed by the cam follower,
The slide member has a slope inclined with respect to the direction of the rotation axis, which abuts against the support member and biases the developing cartridge in a direction perpendicular to the direction of the rotation axis. Item 1. The image forming apparatus according to item 1 . further comprising a registration roller which is the closest transport roller to the photosensitive drum among the transport rollers arranged on the upstream side of the photosensitive drum in the transport direction;
8. The image according to any one of claims 1 to 7 , wherein the sheet sensor is a post-registration sensor provided between the registration roller and the photosensitive drum in the conveying direction. forming device.

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